Photographic processes comprising stepwise control of dye developer diffusibility in alkali



United States Patent Ofiice 3,320,062 Patented May 16, 1967 PHOTOGRAPHIC PROCESSES COMPRHSING STEP.

WISE CONTROL OF DYE DEVELGPER DIFFUSI- BILITY IN ALKALI Edwin H. Land, Cambridge, and Howard G. Rogers, Weston, Mass., assignors to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware N Drawing. Filed July 30, 1963, Ser. No. 298,539

7 Claims. (Cl. 963) This application is a continuation-in-part of our copending applications Serial No. 565,135, filed February 13, 1956 and Serial No. 665,807 (now abandoned), filed June 14, 1957, which latter application is, in turn, also a continuation-in-part of said copending application Serial No. 565,135.

This invention relates to photographic diffusion transfer processes, and more particularly to the formation of multicolor diffusion transfer images by stepwise control of diffusibility of the image-forming components in alkali.

It is a principal object of the invention to provide a multicolor photographic image, i.e., in full color, on a single image-receiving surface by an improved method of applying two or more processing liquids to a multilayer film. The photosensitive element or negative is of a type which contains a plurality of color-providing substances and is adapted to be positioned adjacent to the imagereceiving surface. In fulfilling the object of forming images in full color, the process involves the employment of color-providing substances which are held or rendered nondiffusible at the site of a developed latent image during application of a first alkaline processing liquid and which are allowed or caused to diffuse to the imagereceiving surface at other areas during application of a second alkaline processing liquid.

A further object is to provide photographic images in one or more colors by an improved method of applying a plurality of processing liquids of the character described which is adapted to be performed in a hand-held camera.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.

The present invention generally relates to so-called diffusion transfer processes wherein a photosensitive element containing a plurality of selectively sensitized silver halide emulsions and an image-receiving layer are positioned at or are brought into superposed relation, and wherein a processing agent is introduced therebetween to react with substances in the photosensitive element and to form a reverse or positive print in or upon the image-receiving layer. In accordance with a preferred process of the present invention, two or more processing liquids are individually and selectively applied to film-like elements of a multilayer film structure which are either brought to, or which exist in, a substantially integral relationship and, when in said relationship, the applications of said liquids are respectively initiated at internal surfaces or at an internal surface or surfaces and an external surface of the multilayer film and may, for example, be performed substantially or entirely within the confines of a camera. Moreover the liquids may preferably be so applied as to be sequentially imbibed into or otherwise to be sequentially brought into contact with given layers of a multilayer material in a given order. The various forms of the process described herein are particularly useful in forming a print in two or more colors on a single image-receiving surface or sheet in conjunction with a unitary type of color film containing two or more silver halide emulsion layers which are sensitive to different wavelengths or regions of the visible spectrum as, for example, with a film in the form of a multilayer structure of a type described below.

The present process has special advantages in its application to the formation of images in full color. In this connection, for example, a first processing liquid comprising a developing agent provides development of the latent color images in the color-sensitized emulsions and the oxidation product of said development immobilizes, or maintains or enhances the immobility of color-providing substances at the site of said images in a trapping operation while the color-providing substances in unexposed and partially exposed areas, although potentially dilfusible, are also temporarily held in a state of immobility. Upon completion of development, an imagewise distribution of a color-providing substance exists in each emulsion, one portion, in the developed areas, being substantially fixed and the other portion, at undeveloped and partially developed areas, being potentially diifusible and adapted to form reverse images of the developed areas. A second processing liquid is then applied which may be said to serve as a release mechanism for the latter colorproviding substances so that they are individually transferred or diffused to a single image-receiving layer, either in a dye form for providing the desired color or in a form adapted to show color after reaction with another substance at the site of the image-receiving layer.

In one method of performing the process of the present invention, a multicolor photosensitive element is exposed, e.g., in a hand-held camera. After photoexposure, a processing liquid is introduced between the photosensitive element and an image-receiving element which includes an image-receiving layer adapted to receive the transferred color-providing substances to provide a positive image. The processing liquid may appropriately provide a developing agent and be carried in a compression-responsive, rupturable container or pod which is preferably attached to the image-receiving sheet just in advance or to the side of the area of the image-receiving element in which the positive image is to be formed. Pressure is progressively applied to the photosensitive element and the imagereceiving element with the rupturable container positioned therebetween, for squeezing the container and releasing and spreading the processing liquid between said elements. The camera housing serves to shield the film and sheet material from actinic light as may be required and includes a closure or door providing access to the print-carrying sheet material for performance of an additional processing step, if desired, and also for removal of the printcarrying portion of the image-receiving element at the appropriate stage in processing.

After a suitable period has elapsed for permeation of the silver halide emulsions by the processing liquid and at least the development of the latent negative images therein, the external surface of the image-receiving element, at least coextensive with the inner surface upon which the transfer image is formed, is subjected to an application of a second processing liquid which permeates the imagereceiving element to increase the alkalinity provided by the first processing liquid. Assuming, for example, that the first processing liquid has been employed to render selectively immobile a color-providing substance such as a dye or a color coupler adapted to image formation through diffusion and transfer, the second processing liquid comprises a medium for increasing the alkalinity, thereby rendering the color-providing a substance diffusible, in which instance it permeates the image-receiving 3 element and is imbibed into the silver halide emulsions.

The second processing liquid may be released under compression and applied from a second liquid container which could, for example, be incorporated with a second or spreader sheet, or it may be applied by opening the previously mentioned door of the camera and spreading the liquid across the outer surface of the image-receiving element by means of an applicator or swab, preferably a width similar to that of the image-receiving element so that the entire section may undergo a liquidtreatment with one passage of the applicator thereacross. After application of the second processing liquid, the section of the image-receiving sheet containing the positive colored image may be removed from other portions of said sheet, the section, at the same time, being stripped from the photosensitive element, and perforations preferably being provided surrounding the image area for this purpose. Alternatively, the photosensitive element and receiving sheet areas employed in forming the image may be removed from the camera and, while maintained in the form of a sandwich, have the second processing liquid applied thereto or be immersed in said liquid.

The base for said elements may be either an opaque or a transparent layer formed, for example, of a paper or a transparent .cellulosic material. The positive imagecarrying sheet is preferably a baryta-coated paper and the image-receiving layer may be composed of polymers well known in the art for receiving dye images by transfer. If the positive image is to be in the form of a transparency, the image-receiving layer and support therefor could be composed of or comprise suitable transparent materials, an additional removable opaque layer or sheet being provided across the back of the support, said opaque layer or sheet being removed after completion of that stage of processing where exposure of photosensitive materials of the film to light entering from the rear is no longer a consideration.

Mention has previously been made of the embodiment wherein a first processing liquid is introduced to and spread between the exposed blue-sensitive emulsion of the film and a substantially coextensive facing area of the image-receiving layer upon which the positive image in full color is to be formed. A second processing liquid is then introduced to and spread between the back of the image-receiving element and a third element or spreader sheet substantially superposed and aligned with the areas contacted by said first processing liquid.

The first processing liquid is releasably carried in a rupturable container which is attached to the imagereceiving surface of the image-receiving element, and a second rupturable container is attached to the other side of said element, at a location which is preferably slightly offset longitudinally with respect to the positition of the first-named container, although the offset condition is not absolutely necessary if other means are employed to provide selective release of the contained liquids. The pressure-applying means serve to rupture the first container and to spread the first processing liquid between a photographically exposed area of the negative and a facing area of the image-receiving surface, when said negative and receiving sheet are metered between said rollers. The pressure rollers also cause the second container to rupture so that the second processing liquid is spread between the back of the image-receiving sheet and said spreader sheet, the latter preferably being substantially impervious to said second processing liquid. The aforesaid offset position of the second container with respect to the first container provides a time delay in the application of compressive force to the film and sheet assembly and a similar delay in the release and spreading of the second processing liquid relative to the first processing liquid.

The construction of suitable liquid containers for the purposes of the present process are described in U.S. Pat- 4 ents No. 2,543,181 and No. 2,634,886, issued to Edwin H. Land. The use of a plurality of liquid containers in a diffusion transfer reversal process is disclosed in U.S. Patent No. 2,607,685, issued to Edwin H. Land.

The door of the camera permits access to the area of the receiving sheet which carries the color print. After application of the second processing liquid and a given imbibition period, the door may be opened and the section containing the color print may be removed from other portions of said sheet, perforations preferably beingprovided for said removal.

Various other image dye forming components (e.g., color couplers, dye developers, coupling dyes, reducible dyes, etc.), and developing agents are adapted to be used in this process. The use of the dye developers, i.e., dyes which also are silver halide developing agents, to form color transfer images are disclosed and claimed in U.S. Patent No. 2,983,606 issued to Howard G. Rogers. Coupling dyes are complete dyes which are capable of coupling with the oxidation product of a color developer, e.g., diethyl-p-phenylene diamine, to form an immobile dye, as disclosed in U.S. Patent No. 3,087,817 issued to Howard G. Rogers. The desired imagewise distribution of the diffusible color-providing substance results from the immobilization of the coupling dye in situ with the developed image as a result of the coupling reaction. Preferably, the coupling dye possesses the requisite color and may be utilized in the image-receiving layer without further reaction.

Dyes, i.e., coupling dyes, which are particularly suited for reaction with an oxidation product of a color developer are found in those dyes having an open position on a ring, which position is para to a hydroxyl or an amino group, or those dyes having a reactive methylene group. Many suitable dyes coming within this classification are found among the azo, pyrazolone and triphenyl methane dyes, as is well known in the art.

Another type of useful coupling dye comprises dyes having a substituent which is displaceable by reaction with oxidized color developer. Examples of such dyes are open chain reactive methylene compounds having an azo substituent attached to the reactive methylene group, compounds having a heterocyclic system containing an azo substituted methylene group and an adjacent carbonyl group as part of the ring structure, and phenolic compounds having an azo substituent attached to the phenol nucleus in a position para to the hydroxyl group; see U.S. Patents 2,453,661; 2,455,169; 2,455,170, and 2,521,908. By suitable selection of compounds of this type or by the addition of solubilizing groups, one may have a dye which is diffusible but which may be rendered immobile by reaction with the oxidized developer. Thus, one may place the solubilizing groups, e.g., sulfo, on the azo substituent. In exposed areas, the coupling reaction with oxidized developer would thus remove the solubilizing groups and give an immobile product, While the dye in unexposed areas would remain capable of being transferred by diffusion.

Assuming the inclusion of coupling dyes, the first processing liquid, or a layer permeated thereby, may comprise a weak alkali such as sodium carbonate or sodium phosphate. The weak alkali permits development of the latent images by the developing agent at a pH so low that diffusion will not occur and thus prevents mobility of the dyes during development. The developing agent reduces the mobility of the dye and effectively traps it at the site of the developed latent image by coupling therewith to form a substantially immobile reaction product. The second processing liquid or a layer permeated thereby comprises a stronger alkali such as sodium hydroxide and serves as the release medium or mechanism. Upon imbibition of the respective emulsions, the dye is exposed and unexposed areas of each is reduced substantially without discrimination and a medium is provided in which the dye is ditfusible and in which it undergoes an imagewise diffusion in unexposed and partially exposed areas, only. Dye at the site of the developed image is prevented from diffusing in response to the second processing liquid and is effectively trapped because the first processing liquid has rendered it a reaction product which is substantially nondiffusible with respect to the second processin liquid.

Alternatively, the first processing liquid could contain a developing agent and an immobile salt-forming reagent, i.e., barium or calcium hydroxide. The second processing liquid would then include a reagent containing a source of sodium ions which forms a mobile salt of the dye and renders it difiusible.

In another example of the process, the color-providing substances of the emulsions may constitute color couplers which are non-diffusible with respect to a first relatively weak alkaline processing liquid comprising a color developing agent which is imbibed into the multilayer film. The couplers couple with an oxidation product of the developing agent at the site of a latent image, during development of said image so that they are rendered substantially insoluble relative to a second processing liquid and are effectively trapped at said site. A second processing liquid provides a relatively stronger alkaline solution wherein unreacted couplers may imagewise diffuse to the image-receiving surface.

Several other methods may be employed for applying the processing liquids to the photosensitive and imager'eceiving elements. For example, the first processing liquid could be applied to the exposed photosensitive element. After a suitable period, the second processing liquid would be applied, by swabbing, immersing or other procedures, including the use of rupturable containers. The photosensitive element may be rinsed if desired prior to application of the second processing liquid.

If an oxidizing agent is required, it may be applied in solution or may be incorporated in a layer of the receiving sheet, being released by a suitable solvent. the developing agent and alkali employed to effect diffusion may be incorporated wit-h and released from given layers of the film or of an image-receiving layer, e.g., the developing agent, for example, being contained in the negative emulsions and the alkali being contained in a layer of the image-receiving layer.

In the preferred embodiment, complete dyes in the form of dye developers are employed, that is, complete dyes which have a developing function and which may, for example, be rendered effective to develop exposed silver halide before unoxidized dye developer is rendered diifusible. One method of accomplishing this result is by the use of a first processing liquid containing a weak alkali capable of effecting development but not transfer, followed by a second processing liquid containing a strong alkali to effect transfer. The dye developers could appropriately be contained in the emulsion layers or other layers of the multilayer film and be release-d for performing their function by imbibition of processing liquids containing suitable solvents by any of the methods described herein. Appropriate dye developers for use in a diffusion transfer reversal process are described in the aforementioned copending application of Edwin H. Land and Howard G. Rogers, Serial No. 565,135.

It would also be' possible to employ a photosensitive screen for providing colored images in another modification of the diffusion transfer reversal process of the present invention. The photosensitive screen would supplant the multilayer films containing color-providing substances ofthe form shownv herein. A photosensitive screen of the type contemplated is described in US. Patent No. 2,968,554 issued to Edwin H. Land.

By the term color-providing substance or image dye-providing substance as employed herein is meant any type of reagent which may be used, either per se (i.e., a complete dye of the desired color) as the image dye or as an intermediate in preparing said image dye during Similarly,

the photographic process. Accordingly, the term comprises color-formers or couplers which react with the oxidation product of an aromatic amino silver halide developing agent to produce dyes, as Well as complete dyes per se and forms thereof such as the reducible dyes, coupling dyes and dye developers, hereinbefore described, or any other substances adapted to use in conjunction with the processing liquids applied in accordance with the present invention.

The image-receiving material may be provided as a transparent material. In such an instance, the film and image-receiving material could be supplied from one chamber as a completely integral unit with one or more liquid containers pre-positioned between the surfaces, as described herein. This construction would permit photographic exposure of the emulsion or emulsions through the transparent image-receiving material.

Where the opening of the camera door or similar exposure to light prior to completion of the process is a required step, it might be necessary to incorporate a dispersion of an opaque substance with the first processing liquid of a type which would prevent the entrance of actinic light through the edges of the emulsion layers or between the edges of the film and image-receiving sheet during development, but which would neither remain upon nor permeate the image-receiving layer of said sheet nor affect the positive image formed thereon. Alternatively, the first processing liquid or another processing liquid could contain a substance which renders the photosensitive emulsions insensitive to actinic light after the photographic exposure and prior to admitting light to the materials during a processing step.

The following example is intended to illustrate this invention and is given for purposes of illustration only. All percentages are by weight unless otherwise stated.

Example An integral multilayer photosensitive element was prepared by coating a gelatin-coated film support with the following coating solutions, in sequence with intermediate drying of the preceding layer:

(1) Cyan dye developer layer-coating solution comprising 4.5% of 1,4-bis-[B-(2,5dihydroxyphenyl)-isopropylaminoJ-anthraquinone; 0.8% Resoflex R-296 (trade name for an alkyl resinous plasticizer produced by Cam-.

bridge Industries Company, Inc., Cambridge, Massachusetts) and 4% cellulose acetate hydrogen phthalate in a 1:1 mixture, by volume, of acetone and tetrahydrofuran.

(2) Red-sensitized silver halide emulsion coating.

(3) Barrier layer-coating solution comprising 2% of cellulose acetate hydrogen phthalate and 0.75% of cellulose acetate in acetone.

(4) Spacer layer-coating solution comprising 2% polyvinyl alcohol and a small amount of Antarox Dl00 (trade name of the Antara Chemical Division of General Dyestuff Corp, New York, NY. for a nonionic surface active agent).

(5) Magenta dye developer layer-coating solution comprising 1.75% of 2-[p-(2',5'-dihydroxyphenethyl)-phenylazo]-4-n-propoxy-l-naphthol, 0.4% of Resoflex R-296 and 4% of cellulose acetate hydrogen phthalate in a 1:1 mixture, by volume, of acetone and tetrahydrofuran.

(6) Green-sensitized silver halide emulsion coating.

(7) Barrier layer-coating solution comprising 2% cellulose acetate hydrogen phthalate and 0.5% cellulose acetate in acetone.

(8) Spacer layer-coating solution comprising 1.5% polyvinyl alcohol and a small amount of Antarox D-l 00.

(9) Yellow dye developer layer-coating solution comprising l.5% of 1-phenyl-3-N-n-hexyl-carbamyl-4-[-p-(2',

. 5-dihydroxyphenethyl)-phenylazo]-5-pyrazolone and 4% cellulose acetate hydrogen phthalate in tetrahydrofuran.

(10) Blue-sensitized silver halide emulsion. The photosensitive element was exposed and an aqueous processing solution approximately 0.0036". thick comprising:

Water cc 100 Sodium carbonate g 10.0 Sodium hydroxide -L g 0.6 Sodium carboxymethyl cellulose g 4.5 1-phenyl-3-pyrazolidone g 1.2 -nitrobenzimidazole nitrate g 0.12 2,5-bis-ethyleneimino-hydroquinone g 0.9

was applied as the exposed photosensitive element was brought into superposed relationship with an image-receiving element The latter element comprised a cellulose acetate-coated baryta paper which had been coated with a 2:1 mixture, by weight, of polyvinyl alcohol and poly-4- vinylpyri-dine. After an imbibition period of approximately two minutes, the image-receiving element was separated and contained only a trace of pink color. The thusdeveloped photosensitive element was then brought into superposed relationship with a fresh portion of the same image-receiving sheet, as a layer approximately 0.0040 thick of a solution comprising:

Water cc 100 Sodium hydroxide g 4.0 5-nitrobenzimidazole nitrate g 2.0

was spread therebetween. After an imbibition period of approximately two minutes, the image-receiving element was separated and was found to contain a good multicolor positive image.

It will be understood that the image dye-providing substances, e.g., the dye developers of the above examples, may be incorporated in the image-receiving element in the form of a dispersion in gelatin or other polymer, e.g., the dye developer is dissolved in a water-immiscible solvent and the resulting solution is dispersed in gelatin. It is also contemplated to use other types of interlayers, e.g., gelatin or polyvinyl alcohol.

It is also contemplated to effect processing of dye developer containing negatives in the presence of a quaternary ammonium compound which is capable of reacting with the oxidized dye developer to form a still less diffusible product. The use of quaternary ammonium compounds in dye developer transfer processes is disclosed and claimed in the copending application of Milton Green and Howard G. Rogers, Serial No. 50,851, filed August 22, 1960, now U.S. Patent No. 3,173,786 issued March 16, 1965.

The first processing liquid preferably contains an auxiliary or accelerating developing agent (or is supplied with such an agent by dissolution thereof from a layer of the photosensitive element) which is substantially colorless, at least in the unoxidized form, as disclosed in said U.S. Patent No. 2,983,606.

By way of recapitulation, one may control the diffusion availability of nonimmobilized color-providing substances by developing the latent images at a pH, e.g., about to 12.5, which is low enough to permit development to occur without rendering nonimmobilized color-providing substances diffusible, and thereafter providing an alkali capable of providing a sufficiently higher pH, e.g., about 13 to 14, at which the nonimmobilized color-providing substances are rendered diffusible. It will be understood that the respective pH levels for use with particular colorproviding substances may vary, depending upon the diffusibility effects of the particuar alkali, i.e., different alkalies providing the same pH may result in different diifusion rates for a given color-providing substances. Thus, one may use a weak alkali such as sodium carbonate or phosphate to initiate development without rendering the colorproviding substances dilfusible. After a suitable interval, a stronger alkali such as sodium hydroxidemay be released to render the nonimmobilized color-providing substances diffusible. One may omit barrier layers between each emulsion layer and its associated color-providing substances, where development of the several emulsions is accomplished substantially simultaneously, followed by introduction or release of the stronger alkali to render diifusible the several nonimmobilized color-providing substances.

One may introduce the stronger alkali by application subsequent to the application of the weak alkali. Thus, one may use a film unit containing two pods or containers, rupture of one such container being utilized to apply the weak alkali followed by rupture of the second container after a suitable interval to apply the stronger alkali. Such a two-stage application may be modified by having the liquid processing composition contained in the first ruptured container merely an aqueous composition effective to permeate the photosensitive element and release a weak alkali contained therein. One may also incorporate the strong alkali in the integral multilayer photosensitive element in such a way as to be slowly released by the action of a liquid processing composition containing a weak alkali.

A further method of utilizing a weak alkali to initiate development followed by the introduction of a strong alkali to render the nonimmobilized color-providing substances diifusible utilizes an outermost layer which permits water, but not an alkali, to pass through. The water of the liquid processing composition permeates this layer and solubilizes a weak alkali present in the photosensitive element, whereby development of the latent color record images is initiated. This outer layer reacts slowly with a strong alkali initially present in the liquid processing composition and, after an interval of time sufiicient to permit the necessary minimum development, becomes sufliciently permeable to the strong alkali to permit it to permeate the photosensitive element and render the nonimmobilized color-providing sustances dilfusible. Such a layer may be a thin layer of cellulose acetate or cellulose nitrate, which is slowly saponified by the strong alkali. Another suitable material is a polymeric substance containing a slowly alkali-soluble material, such as the previously mentioned benzoic anhydride-containing polymers.

Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A diffusion transfer process for forming multicolor images comprising the steps of exposing a photosensitive element containing blue-sensitive, green-sensitive and redsensitive silver halide emulsions, said emulsions having associated therewith, respectively, a yellow image dye providing substance, a magenta image dye providing substance, and a cyan image dye providing substance; applying to said exposed photosensititve element a processing composition providing a pH of about 10 to 12.5 at which said image dye providing substances are substantially nondiffusible; developing said exposed silver halide emulsions at said pH, and, as a function of said development, reacting said image dye providing substances in developed areas to thereby provide an imagewise distribution of image dye providing substances associated with each of said silver halide emulsions; and thereafter increasing the pH to a level at which said imagewise distribution of image dye providing substances is rendered diffusible, and transferring, by diffusion, at least a portion of said diifusible image dye providing substances to a superposed image-receiving element to impart thereto a positive multicolor image, each said image dye providin substance being a dye developer.

2. A process as defined in claim 1, wherein said pH is increased by application of a second processing liquid containing a stronger alkali.

3. A diffusion transfer process for forming multicolor transfer images comprising the steps of exposing a photosensitive element containing blue-sensitive, green-sensitive and red-sensitive silver halide emulsions, said emulsions having associated therewith, respectively, a yellow image dye providing substance, a magenta image dye providing substance, and a cyan image dye providing substance; applying an aqueous alkali metal carbonate solution to said exposed photosensitive element to eflect development thereof without rendering said image dye providing substances difiusible out of said photosensitive element, and, as a function of said development, reacting said image dye providing substances in developed areas to thereby provide an imagewise distribution of image dye providing substances associated with each of said silver halide emulsions; thereafter applying an aqueous alkali metal hydroxide solution wherein said image dye providing substances are diffusible from said photosensitive element; and transferring at least a portion of each of said imagewise distribution by diffusion through said alkali metal hydroxide solution to a superposed imagereceiving layer to impart thereto a multicolor positive dye image, each said image dye providing substance being a dye developer.

4. A process as defined in claim 3, wherein said alkali metal carbonate is sodium carbonate.

5. A process as defined in claim 3, wherein said alkali metal hydroxide is sodium hydroxide.

6. A process as defined in claim 1, wherein said processing composition is applied by being spread between said exposed photosensitive element and said image-receiving elements as said elements are brought into superposed relationship, and a second processing composition is applied to the external surface of the thus-superposed imagereceiving element to increase said pH.

7. A process as defined in claim 1, wherein the developed photosensitive element is brought into superposed relationship with said image-receiving element, and a second processing liquid is spread between said elements as they are brought into superposed relationship.

References Cited by the Examiner UNITED STATES PATENTS 2,607,685 8/1952 Land 9629 2,661,293 12/1953 Land 96-3 2,756,142 7/ 1956 Yutzy 963 2,983,606 5/1961 Rogers 9629 FOREIGN PATENTS 926,462 5/1963 Great Britain.

NORMAN G. TORCHIN, Primary Examiner. J. T. BROWN, Assistant Examiner. 

1. A DIFFUSION TRANSFER PROCESS FOR FORMING MULTICOLOR IMAGES COMPRISING THE STEPS OF EXPOSING A PHOTOSENSITIVE ELEMENT CONTAINING BLUE-SENSITIVE, GREEN-SENSITIVE AND REDSENSITIVE SILVER HALIDE EMULSIONS, SAID EMULSIONS HAVING ASSOCIATED THEREWITH, RESPECTIVELY, A YELLOW IMAGE DYE PROVIDING SUBSTANCE, A MAGENTA IMAGE DYE PROVIDING SUBSTANCE, AND A CYAN IMAGE DYE PROVIDING SUBSTANCE; APPLYING TO SAID EXPOSED PHOTOSENSITIVE ELEMENT A PROCESSING COMPOSITION PROVIDING A PH OF ABOUT 10 TO 12.5 AT WHICH SAID IMAGE DYE PROVIDING SUBSTANCES ARE SUBSTANTIALLY NONDIFFUSIBLE; DEVELOPING SAID EXPOSED SILVER HALIDE EMULSIONS AT SAID PH, AND, AS A FUNCTION OF SAID DEVELOPMENT, REACHING SAID IMAGE DYE PROVIDING SUBSTANCES IN DEVELOPED AREAS TO THEREBY PROVIDE AN IMAGEWISE DISTRIBUTION OF IMAGE DYE PROVIDING SUBSTANCES ASSOCIATED WITH EACH OF SAID SILVER HALIDE EMULSIONS; AND THEREAFTER INCREASING THE PH TO A LEVEL AT WHICH SAID IMAGEWISE DISTRIBUTION OF IMAGE DYE PROVIDING SUBSTANCES IS RENDERED DIFFUSIBLE, AND TRANSFERRING, BY DIFFUSION, AT LEAST A PORTION OF SAID DIFFUSIBLE IMAGE DYE PROVIDING SUBSTANCES TO A SUPERPOSED IMAGE-RECEIVING ELEMENT TO IMPART THERETO A POSITIVE MULTICOLOR IMAGE, EACH SAID IMAGE DYE PROVIDING SUBSTANCE BEING A DYE DEVELOPER. 